Present pen-changing mechanisms generally employ a device such as a turret for performing pen changing operations. Generally, the turret is rotated to permit the fetching and depositing of the pens. To perform the rotation, a motor, solenoid or other similar rotational device is usually employed. However, inclusion of such rotational devices in a plotter or other apparatus adds undesirable weight, mass and inertia to such apparatus. Also, the pens in the turret often tend to dry out as a result of exposure to air. What is needed and desirable, therefore, is an apparatus that performs pen changing without the need for special pen-changing motors, solenoids, turrets and the like, and that prevents drying of the writing tips of the pens.
Thus, according to the illustrated preferred embodiment of the present invention, an automatic pen-changing apparatus is provided, in an X-Y plotter system, which utilizes the motors that drive the head (i.e., the motors that ordinarily move the head to position coordinates) to also perform pen-changing operations and to uncap and cap the pens before and after use, respectively. This obviates the need for turrets and the like and for pen-changing motors or solenoids for operating the turrets.
The apparatus includes a plot head capable of fetching, holding and depositing a pen, a pen repository having stations for storing, capping and uncapping pens and for detecting the status ("unoccupied" or "occupied" by one or more pens) of the plot head and of the stations, a memory for storing user-supplied pen-identifying data, a processing means for providing position coordinates corresponding to an unoccupied station and to the station identified by the user-supplied data, and a control means for moving the plot head to the position coordinates, the movement to said coordinates causing the plot head to deposit its pen into the unoccupied station and to fetch a pen from the station corresponding to the user-supplied data.